Isolated Acromioclavicular Joint Septic Arthritis: A Case Report and Review of Literature

A 60-year-old diabetic patient presented with acute pain and swelling localized to the left acromioclavicular joint. Laboratory and radiological investigations revealed the presence of pus in the left acromioclavicular joint along with bony erosion of the lateral end of the left clavicle. She was treated with open arthrotomy, debridement, and appropriate antibiotics for the causative methicillin-resistant Staphylococcus aureus (MRSA) infection. Prompt diagnosis and timely intervention can reduce the morbidity and mortality due to septic arthritis. We conducted a review of the literature on patients treated for isolated septic arthritis of the acromioclavicular joint.


Introduction
Septic arthritis is a serious orthopedic emergency that often occurs in large joints.Even though acromioclavicular septic arthritis is uncommon, it can affect elderly individuals with compromised immune systems.Several clinical conditions, such as trauma, surgery, intra-articular injection, osteoarthritis, and intravenous drug abuse, and systemic conditions like diabetes mellitus, HIV infection, rheumatoid arthritis, and corticosteroid drug usage, can predispose to septic arthritis.Acromioclavicular septic arthritis can be misinterpreted as septic arthritis of the glenohumeral joint or degenerative disease near the latter.Existing literature on it is limited to a few case reports only.

Anatomy of the acromioclavicular joint
The acromioclavicular joint is a plane synovial joint articulation in the shoulder region between the acromion of the scapula and the lateral end of the clavicle.Two unusual features of the acromioclavicular joint are fibrocartilage lining the articular surfaces and a partially divided joint cavity caused by an articular disc.The joint capsule encloses the two articular surfaces of the acromioclavicular joint.It consists of a loose layer of fibrous tissue and an interior lining made of synovial membrane.The fibers of the trapezius muscle give support to the posterior aspect of the joint capsule.The acromioclavicular joint is supported and stabilized by three ligaments -acromioclavicular ligament, conoid ligament, and trapezoid ligament.In addition to allowing gliding motion in the superior, inferior, and anteroposterior planes, the acromioclavicular joint also has a limited degree of axial rotation.

Case report
A 60-year-old lady with uncontrolled type 2 diabetes presented with left shoulder pain and swelling of a one-week duration.She had a history of fever for three days.There was no history of recent trauma.She was treated for probable rotator cuff tendinitis with interferential therapy for five days without any relief of pain.On examination, she was febrile.The left acromioclavicular joint region was swollen, tender, and warm with surrounding erythema.Shoulder abduction, forced adduction, and crossed abduction were significantly limited due to pain though rotations were painless.The total leucocyte count was 14,100/cu.mmand blood glucose measured 427 mg/dl.The inflammatory parameters ESR and CRP were 75 mm/1st hour and 113 mg/L, respectively.Increased soft tissue shadows and erosion at the superior aspect of the left clavicle were seen in the radiograph without any sign of periosteal reaction (Figure 1).

FIGURE 1: X-ray left shoulder
Increased soft tissue shadow above the acromioclavicular joint and widening of the joint The ultrasound scan reported mild acromioclavicular joint arthropathy with diffuse subcutaneous edema in the left supra-clavicular region with interfascial plane fluid.
Magnetic resonance imaging revealed irregularities in the acromioclavicular joint surface, with fluid collection measuring 8.7 x 1.4 x 1.4 cm between the supraspinatus and trapezius muscles (Figure 2).The patient was started on empiric treatment with Inj.piperacillin-tazobactam 4.5 g thrice daily after needle arthrocentesis.However, as there was no clinical improvement after 48 hours, an open arthrotomy of the AC joint and debridement were performed through an anterolateral approach.The patient was placed in the supine position, with a sandbag under the spine and medial border of the scapula.A transverse incision from the anterolateral corner of the acromion to just lateral to the coracoid process was made.After deepening the incision through the subcutaneous fat to the deep fascia, the deltoid muscle was detached at a point well proximal to the nerve supply.An incision was made over the deep fascia along the line of the skin incision to visualize the AC joint.
The arthrocentesis and arthrotomy samples grew methicillin-resistant Staphylococcus aureus (MRSA) infection.Linezolid 600 mg intravenously twice a day was given parenterally for two weeks, followed by oral antibiotic therapy for six weeks.By 8 weeks, the inflammatory parameters showed progressive improvement, and antibiotics were discontinued.At the three-month follow-up, the patient reported no pain in the left shoulder, with a restriction of terminal 30 degrees of abduction.

Discussion
Acromioclavicular joint septic arthritis is a rare entity that can affect elderly individuals with compromised immune systems.Usually, acromioclavicular joint septic arthritis co-exists with septic arthritis of the shoulder joint, so the actual incidence of AC joint septic arthritis alone is unknown [18].The patients usually present with pain over the shoulder with overhead activity or with cross-body arm adduction.On examination, patients have pain on direct palpation of the AC joint.
Only a few case reports have been reported so far in the English literature.Patients with septic AC arthritis frequently present later than expected because of misdiagnosis as pyomyositis or underdiagnosis.The patients' ages ranged from 9 to 79 years old, with a mean age of 52.66 years.Among those patients, 26 were over 50, and 11 were under 50.The duration of the presentation varied from six hours to three months.Of the cases, 75.6% (28 out of 37) were male.Of the 23 cases, 13 were on the right side and 10 were on the left.Twenty-one out of the 35 cases (55.2%) occurred in individuals with weakened immune systems like diabetes mellitus.Three out of 37 cases were intravenous (IV) drug abusers.Other predisposing factors described were HIV, renal failure, cirrhosis, lymphomas, myeloma, rheumatoid arthritis, and cytotoxic chemotherapy.
Staphylococcus aureus was the most frequently detected pathogen followed by streptococcus pneumoniae, especially in hematologic malignancies.MRSA (4), Streptococcus pneumonia(2), Streptococcusagalactiae (2), Streptococcus viridians (1), Group B streptococcus(1), Ochrobactrumanthropi, and Haemophilusinfluenzae were among the other organisms described as causative agents in literature.Most of these patients show positive blood cultures indicating a hematogenous spread.
Since the AC joint is a smaller joint, septic arthritis can be very damaging.To avoid morbidity, a high degree of suspicion must be raised for an accurate and prompt diagnosis.It can be difficult to differentiate painful limited shoulder motion in these patients from glenohumeral involvement because they often have limited shoulder motion in both active and passive motion.The location of the anterior shoulder pain and the boggy feeling over the acromioclavicular joint, which is caused by surrounding pyomyositis, suggest the diagnosis.
In 82.6% (19 out of 23) of the cases, leucocytosis was present.Inflammatory parameters were elevated in 50% of cases.X-rays have revealed an enlargement of the AC joint and deterioration of the surrounding bone.Ultrasound can guide joint aspiration and can detect joint effusion in the AC joint.Magnetic resonance imaging (MRI) and ultrasound offer a more accurate and sensitive diagnosis early on than conventional Xrays.MRI and ultrasound allow us to make an earlier diagnosis and evaluate the regional spread of the infection.Greater tissue definition, early damage detection, sensitivity, specificity, and operator independence are all features of magnetic resonance imaging [12].It reveals thickening of the joint capsule, synovium, and apparent expansion of the joint space.So, MRI is crucial for early diagnosis, detecting osteomyelitis, assessing rotator cuff integrity, and assessing glenohumeral joint involvement [15].
Since arthrocentesis offers quick confirmation and directs treatment, it is the gold standard for diagnosing AC septic arthritis.Joint aspiration followed by saline infiltration may be used to know the shoulder joint extension.However, the bony anatomy of the joint may make it technically difficult to obtain a substantial aspirate for microbiological diagnosis [15].Once a microbiological diagnosis is made, appropriate antibiotic therapy needs to be selected.
Treatments for septic arthritis of the AC joint that have been demonstrated to be successful include aspiration of the joint, joint irrigation, surgical debridement, and resection of the lateral end of the clavicle or AC joint along with an IV or oral antibiotic course.Adequate drainage of the joint and administration of antibiotics is the mainstay treatment for acromioclavicular joint septic arthritis [19].The minimum duration of antibiotic use should not be less than four weeks [20].Surgical debridement, whether it be open or arthroscopic, provides the most comprehensive debridement of any associated pyomyositis and subacromial or subdeltoid extension in addition to the AC joint.Conventionally distal clavicle excision is suggested during debridement of acromioclavicular joint septic arthritis [21,22].Out of these patients, 41.6% had surgical debridement, 37.8 % had medical management, and 21.6% had aspiration followed by antibiotic treatments.Adams and McDonald reported a patient with sarcoidosis and cryptococcal arthritis of the AC joint that was treated with irrigation and debridement, distal clavicle excision, and IV antibiotics [23].They did a resection of the whole AC joint instead of a simple resection of the distal clavicle.On average, six weeks of appropriate antibiotics provide successful clinical results.

Conclusions
Acromioclavicular joint septic arthritis is a rare condition that occurs in individuals with compromised immune systems.Various immunodeficient conditions predispose a patient to septic arthritis of the acromioclavicular joint.For an early diagnosis, a thorough clinical assessment of the AC joint is necessary.The diagnosis is confirmed via a combination of laboratory test findings and modern imaging investigations.Aspiration of the AC joint, joint irrigation, surgical debridement, and resection of the lateral end of the clavicle or AC joint combined with an IV or oral antibiotic course are effective treatments for septic arthritis of the acromioclavicular joint septic arthritis.Timely diagnosis and treatment with appropriate antibiotics are essential to prevent morbidity and sepsis.

FIGURE 2 :
FIGURE 2: MRI left shoulder showing the fluid collection in the acromioclavicular joint (AC) tracking inferomedially 2-a) Axial cut showing abscess arising from the AC joint.2-b) Sagittal cut showing destruction of the cartilage of the AC joint with the abscess traveling superior to the supraspinatus muscle.2-c) Coronal cut showing the abscess arising from the AC joint superior to the supraspinatus muscle with the resultant muscle atrophy; the infraspinatus muscle was not involved.

and amoxicillin for 8 2024 4 weeks
acromioclavicular joint and drained to the skin.Aspiration was done and no organism was recovered from the joint aspirate.Surgery was performed to remove the abscess and to wash and debride the joint.A coagulase-negative S. aureus was recovered from the surgical specimens.Healed 2024 Ramanan et al.Cureus 16(7): e63590.DOI 10.7759/cureus.withDCE.Required to repeat open I&D on postoperative day 2. IV nafcillin for 6 weeks followed by one month of trimethoprim Ramanan et al.Cureus 16(7): e63590.DOI 10.7759/cureus.amikacin)was started.After the pus culture report, ceftriaxone was stopped and erythromycin was started.IV antibiotics were continued for 2 weeks followed by a period of with IV vancomycin and IV piperacillin-tazobactam, changed to oxacillin and I&D was repeated after 2 2024 Ramanan et al.Cureus 16(7): e63590.DOI 10.7759/cureus.increasingpain and swelling of the SCM muscle, an MR scan revealed fluid collection on STIR images in the SC joint, edema of the proximal bone, and liquefaction of the entire SCM muscle from the SC joint to the base of the skull, then 2 weeks of oxacillin IV followed by 4 weeks of outpatient ceftriaxone IV 2 g per day.evaluate for endocarditis, which was negative for any significant findings or vegetation NA

Table 2
lists the results of our review of the literature on septic acromioclavicular arthritis.